The long term goal of the proposed research is to understand the rules governing recombination between repeated eukaryotic genes; the organism that will be used in these studies is the yeast Saccharomyces cerevisiae. This organism is particularly useful for the proposed studies since the development of the yeast transformation procedure allows construction of haploid yeast strains with duplicated copies of selectable genes. Five specific areas of research will be pursued. First, the properties of recombination between repeated genes located on non-homologous chromosomes will be analyzed. The frequency of such events will be examined as a function of the size and location of the repeated sequences. Second, the frequency of recombination between repeated sequences located on the same chromosome will be studies. These experiments will be done in the same genetic background and with the same repeated sequences as the studies involving non-homologous chromosomes; thus, a direct measurement of the relative frequency of these types of events can be made. Third, a genetic system will be developed to look for duplication of genes normally found in one copy per genome. Such events are likely to be important in understanding the origin of repeated gene families. Fourth, mutant strains will be isolated which have either higher or lower rates of recombination between repeated genes. Fifth, the properties of recombination involving transposable elements will be characterized. Since recombination between repeated genes on non-homologous chromosomes can result in translocations and since the activation of cellular onc genes in mammals is often associated with translocations, these studies may lead to insights into health-related problems.